In a conventional inverted microscope, a plurality of objective lenses, a nosepiece holding these objective lenses, and a nosepiece holder that is fixed to a stage and holds the nosepiece through a supporting member are disposed under the stage (see Japanese Patent Application Laid-Open No. 11-38326).
A rack and pinion mechanism is provided between the nosepiece holder and the supporting member. With rotating a focusing knob provided on the nosepiece holder, the objective lens selectively provided on the optical path can be moved up and down so as to focus on a sample. The distance between the objective lens and the stage has to be kept to a distance between the objective lens and the sample upon focusing on the sample.